+ 'b:' => 'match within message body, including text attachments',
+ 'nq:' => 'match non-quoted text within message body',
+ 'quot:' => 'match quoted text within message body',
+ 'n:' => 'match filename of attachment(s)',
+ 't:' => 'match within the To header',
+ 'c:' => 'match within the Cc header',
+ 'f:' => 'match within the From header',
+ 'a:' => 'match within the To, Cc, and From headers',
+ 'tc:' => 'match within the To and Cc headers',
+ 'bs:' => 'match within the Subject and body',